1. Field of the Invention
The present invention relates to a cooling fan and, more particularly, to a cooling fan that can conduct air currents to flow in and to flow out through a radial direction of an impeller.
2. Description of the Related Art
Conventional cooling fans are mainly divided into two types: axial-flow type and blower type. Each cooling fan of the axial-flow type has an axial air inlet and an axial air outlet thereof opposite to each other in the axial direction, which can conduct airflows directly flowing in and flowing out via the axial air inlet and the axial air outlet to dissipate heat. On the other hand, each cooling fan of the blower type has an axial air inlet in the axial direction, and a radial air outlet in the radial direction thereof, which can dissipate heat by inhaling air through the axial air inlet and sequentially exhaling air via the radial air outlet.
However, cooling fans of the axial-flow type can not provide radial heat-dissipation, because there is no passageway of airflows in the radial direction. Therefore, cooling fans of the axial-flow type have to be disposed on the heat source, for example, at the top of the central processor of a personal computer, when it is practically used in any electric equipment. In this situation, the axial height of the electric equipment needs to be maintained at a proper range for the axial-flow cooling fan to be axially mounted on the heat source, which leads to difficulty in axial miniaturization of the electric equipment. Yet, cooling fans of the blower type are not suitable for using in electric equipments that only allow for radial airflow-circuit, such as mobile phones and personal digital assistants, due to the allocations of the axial air inlet in cooling fans of the blower type.
Accordingly, the other type of conventional cooling fan, capable of inhaling and exhaling air flowing in a radial direction of an impeller, is designed in order to adapt to electric equipments that only allow for radial airflow. As shown in FIG. 1, a first conventional cooling fan 8 disclosed in Taiwan Patent No. 553323 and entitled “FAN STRUCTURE HAVING HORIZONTAL CONVECTION” comprises a housing 81 and an impeller 82. The housing 81 has at least one air inlet 811 and at least one air outlet 812, with a horizontal air-passageway 813 defined between the air inlet 811 and the air outlet 812. The impeller 82 is mounted inside the horizontal air-passageway 813 and comprises a hub 821 and a plurality of blades 822 mounted to the peripheral surface thereof. Accordingly, the difference in air pressure between the air inlet 811 and the air outlet 812, generated by the rotating impeller 82, can facilitate the heat-dissipation by driving air currents flowing from the air inlet 811 through the horizontal air-passageway 813 to the air outlet 812.
However, when the airflows are conducted by the plurality of blades 822 of the impeller 82 and pass through the horizontal air-passageway 813 for air convection, the hub 821 easily disturbs the airflows as well as generates air turbulence due to the location of the hub 821. Hence, the cooling efficiency of the conventional cooling fan 8 is limited.
Also, another conventional cooling fan 9 is described in Taiwan Patent No. 477492, entitled “CONNECTION OF BLOWER FAN” and shown in FIG. 2, comprising a rotor seat 91, an impeller 92 and a housing 93. The rotor seat 91 has a plurality of blocks 911, and the impeller 92 has a plurality of holes 921, with the plurality of blocks 911 respectively coupled to the plurality of holes 921. The housing 93 is used for containing the rotor seat 91 and the impeller 92, and the housing 93 has an air inlet 931 and an air outlet 932. In this way, the rotating impeller 92 propels airflows radially flowing into the housing 93 from the air inlet 931 and sequentially flowing out from the air outlet 932 for heat-dissipation.
Nevertheless, the rotor seat 91 and the impeller 92 are both located in the air passageway between the air inlet 931 and the air outlet 932, which causes air turbulences to easily happen to the airflows conducted by the impeller 92 because of the disturbance of the rotor seat 91. Also, an additional step to assemble the impeller 92 and the rotor seat 91 need to be executed before they are inserted into the housing 93, so that the fabrication of the conventional cooling fan 9 is inconvenient and troublesome.